Pre-crash safety systems (PCS) have been developed as a safety system for avoiding a collision between a vehicle and an obstacle which is present around the vehicle or reducing collision damage. A PCS calculates a time to collision (TTC) which is time until a vehicle collides with an obstacle. Based on the calculated time to collision, the PCS issues an alarm to a driver of the own vehicle or activates a braking apparatus of the vehicle (see, for example, Patent Literature 1). Patent Literature 1 discloses that a risk level indicating a risk of collision between a vehicle and an obstacle is set and according to the set risk level, information is presented to a driver.